Vizio VO42L, white logo, no backlight, no picture

[Daveleone]

Hi all! I've got a Vizio VO42L. Plug it in, and logo flashes orange/white for a bit, then solid orange. Press power, and logo changes to white. There is no backlight.
From reading some of the posts here I thought the inverter could have been the problem, but I've replaced it and still have the same issue. I noted that shining a flashlight on the screen shows nothing, so now I'm thinking main board?

I took the following readings with the TV powered on. I also tried taking the readings with the CFL connectors unplugged - no change.

Main board:
Continuity across F1 & F2 = GOOD
F1 = 5.12v
F2 = 11.57v

PSU Connector 1 (J21?):
24V = 24v
SGND = 0v
A = 0v
B = 0v
C = 0v

PSU Connector 2 (J22?):
PSON= 3.27v
12V = 11.57v
SGND = 0v
5VSB = 5.16v
A = 0v
B = 0v
C = 0v

Inverter:
Continuity across F1 = GOOD
Left leg @ Q7 & Q9 = cycles between 0v-1.2v
Middle leg @ Q7 & Q9 = 24.96v
Right leg @ Q7 & Q9 = cycles between 0v-1.2v
Top leg @ Q8 & Q10 = 0v
Middle leg @ Q8 & Q10 = cycles between 0v-1.2v
Bottom leg @ Q8 & Q10 = 0v
Voltages @ connectors to CFLs = 0v

Do you think I got a second bad inverter? Or do I have a bad main board? What should I try next?

Thanks in advance for your help!
--Dave

[dick_barton]

What voltages do you have on the Inverter Board connector
1, 2, 3, 4 & 5 =
6, 7, 8, 9 & 10 =
11 =
12 =
13 =
14 =

Is the white fuse F1 showing continuity?

[Daveleone]

Originally Posted by dick_barton

What voltages do you have on the Inverter Board connector
1, 2, 3, 4 & 5 =
6, 7, 8, 9 & 10 =
11 =
12 =
13 =
14 =

Is the white fuse F1 showing continuity?

That connector is directly connected to PSU Connector 1 (J21?), so:
1-5 = 24v
6-14 = 0v
I double checked the voltages just to be sure the cable was good.

F1 does have continuity.

[dick_barton]

Can you provide a close up of what's given in the red box please.
The Inverter On signal appears to be missing.

[Daveleone]

Originally Posted by dick_barton

Can you provide a close up of what's given in the red box please.
The Inverter On signal appears to be missing.

Yes, I think you're right.
12: VOnOff is 0V

What should that voltage be? Should I jumper it to some other pin to see if the backlight will come on?

Thanks!

[dick_barton]

You need to check where the VonOff signal comes from. I would expect it to be around 3V when VonOff = On
Have you checked the two fuses shown in photo 6 of 11 in your first post.

[Daveleone]

Originally Posted by dick_barton

You need to check where the VonOff signal comes from.

That wire is connected to "B" on the PSU Connector 1 (J21?) (photo 3 of 11 in my first post)

Originally Posted by dick_barton

Have you checked the two fuses shown in photo 6 of 11 in your first post.

Main board:
Continuity across F1 & F2 = GOOD
F1 = 5.12v
F2 = 11.57v

[Daveleone]

Originally Posted by dick_barton

You need to check where the VonOff signal comes from. I would expect it to be around 3V when VonOff = On
Have you checked the two fuses shown in photo 6 of 11 in your first post.

I jumpered PSU Connector 2 (J22?) 5VSB to PSU Connector 2 "B" (which connects to Inverter Connector VOnOff). The backlight comes on with both inverters that I have. So, the main board appears to be the problem.
Anything else I should check on the main board? Or should I just order a replacement?

[budm]

I would start checking LDO Voltage Regulator IC's on the main board.

There is Main board repair kit and EEPROM also.
https://www.shopjimmy.com/search.php...ery=Vizio+VO42

[Daveleone]

Just to close this out, I was able to get a replacement main board for $20 from ElectroParts, so I decided to order it and save my time (instead of working on the defective board). The replacement main board worked.

[nomoresonys]

Thanks for the feedback Dave.